1. Field of the Invention
This invention relates generally to hand tools, and more particularly to hand tools used to adjust the brake mechanism of a motor vehicle.
2. Description of the Prior Art
Large motorized vehicles such as multiple-wheeled trucks often use air brakes on their rear wheels. A typical air brake assembly includes a mounting bracket, an air brake chamber attached to the bracket, a clevis rod extending from the air brake chamber, and an air brake slack adjustment having one end pivotably supported by the bracket and having its other end pivotably attached to end of the clevis rod. The air brake chamber includes a diaphragm which is exposed to atmospheric pressure on one side and which is coupled to a pressurized air source on its other side. When air pressure is applied to the air brake chamber, the diaphragm causes the clevis rod to extend outwardly from the air brake chamber to pivot the air brake slack adjustment from a non-braking position to a braking position. The distance that the clevis rod moves between the non-braking and braking position is known as the clevis rod stroke.
As the brake linings wear, the air brake slack adjustment must be adjusted to maintain the clevis rod stroke within specified limits. Thus, it is necessary for a large vehicle operator to periodically check and readjust the air brake slack adjustments of the vehicle to maintain the clevis rod stroke within a specified range.
A problem is encountered during the aforementioned procedure in that it is difficult to manually move the air brake slack adjustment between its non-braking and its braking position. Located within the air brake chamber is a strong compression spring which biases the clevis rod towards the air brake chamber and thus its non-braking position. It is very difficult to manually overcome this biasing force and to simultaneously measure the stroke of the clevis rod.
Some maintenance manuals recommend that the mechanic performing the adjustment procedure disconnect the pressure hose from the air brake chamber and connect the air brake chamber to an 80 PSI air pressure source to cause the clevis rod to move to its braking position. This method for moving the clevis rod from its non-braking to its braking position is, however, inconvenient and requires compressors or other special equipment.
Most commonly, a mechanic will attempt to move the air brake slack adjustment with one hand, and measure the length of the clevis rod stroke with a ruler held in his other hand. This tiresome two-handed operation is made even more difficult by the cramped quarters around the air brake mechanism in which the mechanic must work.
What the prior art fails to disclose is a simple, manually operated tool for pivoting the air brake slack adjustment between its braking and non-braking position and for measuring the clevis rod stroke. Furthermore, the prior art does not disclose a pair of tools which allow the clevis rod stroke to be measured and adjusted with one hand.